ANALYSIS AND CONTROL OF HEAD BLACK LINE DEFECT OF COLD ROLLED ULTRA-LOW CARBON STEEL COIL
In response to the frequent occurrence of black line defects within 20～30 m of the head of the ultra-low carbon cold rolling continuous unwinding coil,resulting in a batch of non-conforming products,quality losses,and affecting the delivery time of the order.The defects were analyzed by means of metallographic microscope and scanning electron microscope,and the industrial test was carried out to verify the rolling of intermediate billets with prefabricated defects on the end face of the casting billet,and the cause of the defects was locked.The results show that the appearance of the"black line on the head"defect is obviously different from that of the protective powder,alumina inclusions and bubbles,and it is not connected with the matrix,and is in a separate state,mainly composed of Fe and Al elements,which indicates that the defect is a foreign object.Through the whole process tracing,it is found that after the yield of hot rolling,the cutting head of the ultra-low carbon steel intermediate blank is reduced,and the spraying welding wire cannot be completely removed,and the spraying welding wire of the casting blank marking machine is pressed into the production of this kind of"black line defect".Based on this,the cutting amount of the middle billet of the ultra-low carbon steel hot rolling is controlled at 300 mm,the air pressure of the spraying machine is adjusted to 4 bar,the black line defect of the cold rolling coil head is effectively improved,and the pass rate of the ultra-low carbon steel surface quality is increased by 4.03％.
ultra low carbon steelcold rolled coilhead black linewelding wireintermediate billet
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