Out-of-line annealing means that the recrystallization annealing of hot or cold rolled steel plate is carried out in the bottom type annealing furnace or cover type annealing furnace before entering the hot plating wire line, so that there is no annealing process in the galvanized line. The steel plate must maintain a clean active surface of pure iron, free of oxides and other dirt, before hot dip galvanizing. In this method, the annealed surface oxide sheet is first removed by pickling method, and then coated with a layer of zinc chloride or a mixture of ammonium chloride and zinc chloride solvent for protection, so as to prevent the plate from being oxidized again.
This method is generally the use of hot rolled laminated plate as raw material, the annealed steel plate is first sent to the pickling workshop, with sulfuric acid or hydrochloric acid to remove the surface of the steel sheet oxygen hot galvanizing method. After pickling, the steel plate immediately enters the tank to soak and wait for galvanized, which can prevent the reoxidation of the steel plate. After pickling, water cleaning, squeeze dry, drying, into the zinc pot, the temperature has been maintained at 445-465℃.
Hot dip galvanizing is then oiled and chromed. The quality of hot-galvanized sheet produced by this method is significantly improved compared with that by wet galvanizing method. It is only valuable for small-scale production. Continuous galvanizing production line includes a series of pretreatment procedures, such as alkali degreasing, hydrochloric acid pickling, water washing, solvent coating, drying, etc., and the original plate needs to be annealed in cover furnace before entering the galvanizing line.
Post time: 24-03-23