| 摘要 |
PURPOSE:To prevent temper color generation and enhance corrosion resistance at coating by a mechanism wherein an air ratio within a furnace is lowered when a detected oxygen amount in the vicinity of a steel plate passage in a direct firing type nonoxidizing furnace exceeds a specific amount. CONSTITUTION:An upper limit set value C of O2 concentration is determined by an upper limit value D of a oxidized film and an outlet aimed plate tmeperature T of a direct firing type nonoxidizing furnace 1. If a thickness of a surface oxidized film of a strip 3 is below an upper limit value D, temper color generation or a porous layer generation by a subsequent reducing process is inhibited and corrosion resistance to painting is enhanced. When O2 concentration in the vicinity of a passage of a strip 3 is detected by an O2 microanalisis meter 6 and is subjected to comparative operation with a setting value C by a microamount O2 comparative operator 10 and exceeds a setting value C, a signal for lowering an air ration is issued to an air ratio (air fuel ratio) setting and controlling instrument 7. A controlling instrument 7 controls a flow amount controlling valve 8, 9 of a fuel gas and an air for combustion to lower an air ratio. When an air ratio is lowered to a lower limit value, an aimed plate temperature T is lowered by a plate temperature setting and controlling instrument 12. |
