Mechanism and Countermeasures of “Comets” on Hot Rolled Strip

by Chien Wei Sheng

Publisher - Dragon Steel Corporation

Category - General Novel

It has been a long history of studies on the Rolled in Scales of hot rolled strip. Among them, “Comets” were “very peculiar” because they occurred on the top surface, but on the bottom sur face at the same location under the larger “comets” was a “mirror image” in colors. By visual ca tegorization, Optical Microscope, and Scanning Electron Microscope (SEM) analysis, the defect may be caused by intrinsic slab defect, over-worn work rolls of rough mill, or damaged work rolls of finish mill. This defect formed on a strip, redirecting and slowing cooling water therefore intro ducing regional over-cooling, finally brings itself a Comet-like outlook. Different root causes and solutions were studied in this work. And finally the results have shown the nonconformance rate of “Comets” is declined magnificently.

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