热轧带钢表面质量检测

COGNEX

®

Surface Inspection Systems Division

Hot Strip Mill

Defect Catalog

Index of contents

General survey of Hot Strip Mill (3)

Unique Features (Gray Bins) (4)

Lamination (5)

Edge cracks (8)

Folded strip edge (10)

Roll marks (12)

Mould powder (13)

Shell (15)

Scale Grain similar to Red Scale (19)

Rolled in secondary scale (21)

Divot (Mechanical damage) (22)

Gall (Other rolled - in extraneous matter) (24)

Roll imprint (Bruise) (27)

Hot Strip Scratch (29)

Scale pits (31)

General survey of Hot Strip Mill

Introduction:

Below is a rough diagram of a conventional non-reversing Hot Strip Mill for reference.

The rolling mill is the process, which reduces a hot slab into a coil of specified thickness; the whole processing is done at a relatively high temperature (when the steel is still "red").

Process:

Furnace

The furnace heats the steel “slab” and pushes it onto the roller line. Slabs are approximately 240mm thick and vary in width and length.

Roughing Mill

Once the slab reaches the roughing mill, it is reduced down to as much as 1/10th its original thickness and is called a “transfer bar”. Width is not changed. The process of reducing the slab to a transfer bar is achieved either through single passes of multiple roughing stands or by multiple passes on reversing roughing stands.

Finishing Stands

The finishing stands further reduce the transfer bar into a steel “strip” whose thickness ranges from app. 1mm to as much as 13mm. By the time the strip reaches the surface inspection point (for top inspection), the strip temperature can range anywhere upwards of 950°C.

Cooling Section

The cooling section uses water to cool the strip. By the time the strip reaches the surface inspection point (for bottom inspection), the strip temperature can range anywhere from 300°C to upwards of 700°C.

Down Coilers Cooling Section Finishing Stands Roughing Mill Furnace Hot Strip Mill Example Bottom

Based on Cognex line scan technology with all special developed detection algorithm, there is the unique gray bin feature which enables to use the intensity of the defect as the major information for classification. How does this work?

Unique Features (Gray Bins)

More classification information is possible with gray bin features than with intensity features alone.

Gray bin features provide information about the distribution of gray within a defect. Intensity features only report the maximum and minimum grayscale values in a defect.

Gray bin values can be customized to match the application.

Gray bin values should be chosen based on differentiation of defect classes.

Defect Image Basic Intensity

Features

With Gray Bin

Features

Bright Bins

Dark Bins