| 摘要 |
PROBLEM TO BE SOLVED: To control the quantity of deposition of a phosphate film on a surface even when the phosphate treatment condition is specified by implementing the electrolytic picking in a pre-process of the phosphate film processing of a structural steel after the hot rolling and annealing, and controlling the density of the current running in the structural steel. SOLUTION: An annealed structural steel after the hot rolling is pickled and de-scaled, and subjected to the phosphate film processing and the lubrication film processing to improve the lubrication effect, and drawn and subjected to the plastic forming such as rolling. In a pre-process of the phosphate film processing, a strand-like structural steel 10 is immersed in a pickling solution 13 stored in a pickling solution tank 12 of an electrolytic pickling device, and a pair of upper and lower insoluble electrodes 11, 11 are arranged opposite to each other across the structural steel. The electrodes 11, 11 are energized to remove scales deposited on the surface of the structural steel 10. The quantity of deposition of the phosphate film can be instantaneously changed with excellent accuracy an unified without changing the phosphate film processing condition by controlling the density of the current running in the structural steel 10 to uniform the thickness of the phosphate film.
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