PURPOSE:To increase crack formation in scale, to accelerate the reaction between the scale and pickling fluid so as to increase descaling effect, by, prior to the pickling of steel sheet, blasting both sides of the steel sheet using the granulated slag of a converter as a blasting material. CONSTITUTION:Steel sheet 1 is conveyed into a space between a blasting chamber 14 and a receiving tank 18. Granulated converter slag 12, 12 contained in slag- charging tanks 11, 11 is conveyed through slga-charging gates 13, 13 to blasting pipes 9a, 9a, then blasted through nozzles 10, 10' to both sides of the steel sheet to form cracks in the scale. The granulated slag blown to the steel sheet falls down into the receiving tank 18, and the slag remained on the steel is also blown off with pressurized air injected through a nozzle 23 and falls down into the receiving tank 18. The steel sheet cleaned on both sides thereof is transferred to the next step. The granulated slag collected in the receiving tank 18 is sucked by a pump 22, and is discharged through a slag-discharging duct 21 to the outside.
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