1.What are the principles and functions of an online surface inspection system?
Principle: During high-speed operation on the production line, a high-resolution linear or area-array CCD camera, combined with a special light source (such as an LED linear light source or laser scanning), continuously images the upper and lower surfaces of the strip steel.
Functions:
Detection: Capable of detecting minute pits that are difficult to see with the naked eye in real time (typically detecting defects with a diameter >0.2mm).
Classification: Automatically distinguishes and classifies pits from other defects (such as scratches, rust, and roll marks) using AI image recognition algorithms.
Location and Marking: Precisely records the position of pits in the length and width directions of the roll (in meters), and can mark them with inkjet ink on the edges for subsequent offline fine inspection and processing.
Statistics and Alarms: Generates defect distribution maps, calculates defect density, and issues alarms when levels exceed limits.
2.How are visual inspections and auxiliary optical equipment tested?
Standard Observation Platform: Visual inspection is conducted by experienced quality inspectors on a dedicated, evenly lit inspection table (compliant with ISO standards). This is the most basic and crucial step.
Portable Digital Microscope/Video Microscope: Magnifies suspicious areas (20x - 200x) to observe the microscopic morphology, distribution patterns, and bottom characteristics of the pits, serving as a key tool for preliminary determination of their cause.
High-Intensity Flashlight/Oblique Light Inspection: Utilizing low-angle light illumination creates a clear contrast between light and dark areas on minute uneven surfaces, making it easier to detect fine clusters of pits.
3.How does a scanning electron microscope perform inspections?
Morphological observation: Observe the three-dimensional morphology of the pits under ultra-high magnification (up to tens of thousands of times) to determine whether they are "exploded," "crater-like," or "grind-like."
Energy Dispersive Spectroscopy (EDS): Perform micro-area chemical composition analysis on the pitted area. This is the gold standard for tracing origins.
If elements such as Al, Ca, and Mg are detected within the pits, it usually indicates that inclusions (such as alumina and calcium magnesium aluminate) from the steelmaking or continuous casting process have detached after rolling.
If Fe and O are detected with an oxide scale morphology, it may indicate incomplete descaling during hot rolling, with residual iron oxide scale being pressed in.
If foreign elements such as Si and Zn are detected, it may indicate incomplete filtration of rolling oil or environmental dust contamination.
4.How to quickly screen and locate?
Utilize online inspection system reports or based on roll weight and location information to pinpoint suspicious rolls and areas (in meters).
Mount the unwinding machine or inspection table to locate the marked or suspicious locations.
Use a strong light oblique illumination method for a large-area rapid scan to confirm the presence and approximate extent of pitting.
5.How to make a preliminary judgment based on morphological observation?
Observe using a portable digital microscope at different magnifications.
Random distribution: Possibly inclusions in the raw material or impurities in the rolling oil.
Periodic distribution: Highly suspects fatigue flaking (roll pitting) on the surface of the work roll or support roll; the spacing needs to be measured to calculate the corresponding roll circumference.
Clustering: May correspond to a localized area of inclusion enrichment in the cast billet.
Inspect the bottom of the pits: Is it bright white (fresh metal)? Colored (oxidized)? Are there foreign matter residues?