GI產品鋅渣缺陷成因與改善

The Causes and Improvements of Dross Pick-Up of GI Products

林振華(Jeng Hua Lin)

《鑛冶：中國鑛冶工程學會會刊》 52卷4期 (2008/12) Pp. 105-109

https://doi.org/10.30069/MM.200812_52(4).0010

摘要

連續熱浸鍍鋅線鋅液槽內之主要成份為鋅（99.5％以上）、鋁（0.1-0.3％）及鐵（0.03-0.005％），生產時之溫度控制在460-470℃。如果使用單一鋅槽生產二種產品（GA與GI），在製程轉換及成份的調整過程中，由於自由鋁與自由鐵的結合及底渣（Bottom dross，FeZn_7，δ）還原的過程中，產生大量的浮渣（Floating dross，Fe_2Al_5，η）。因比重較鋅液小，最後會浮在鋅液上層，但是在上浮過程中，受到鋅槽內輥子的擾動影響，流至鋼帶而附著在表面造成產品缺陷，這個產品缺陷稱之為鋅渣附著，無法符合外露產品的品質要求。浮渣的形成有二個階段，第一階段浮渣的反應與鋅槽溫度、自由鋁、自由鐵濃度相關，反應時間大約需2小時。第二階段底渣還原的反應時間則與底渣數量有關，一般需2-3天。避免浮渣造成品質問題之有效對策，包括：鋅液樣本有無Fe_2Al_5之檢驗，N_2攪拌加速底渣還原，析出鐵、析出鋁與溫度之隨時掌控，加鋅作業時Fe、Al與Fe_2Al_5分佈研究應用。

並列摘要

The main chemical contents in the zinc bath of the continuous hot dip galvanizing lines are Zn (99.5%), Al (0.1-0.3%), and Fe (0.03-0.005%). The operating temperature of the zinc bath is set between 460-470℃. When a single zinc bath is used to manufacture two products (GA and GI), a large amount of floating dross is formed from the unification of free Al and free Fe and the bottom dross. Due to the specific gravity of floating dross being less than the specific gravity of zinc liquid, the floating dross will move to the surface of the zinc bath. During this movement, a turbulent flow induced by the pot rolls enables the floating dross adhere to the strip surface. This results in a surface defect unacceptable for high quality steel sheets. There are 2 steps in the formation of floating dross after the GA to GI bath chemistry changes. The first step is the precipitation of Fe_2Al_5 due to the Al and Fe being over the solubility limit and then the second step is the transformation of the bottom dross to the floating dross. To prevent the formation of the floating dross we take the following actions: (1) make sure Fe_2Al_5 does not appears in the zinc sample, (2) use N_2 bubbling to accelerate the reduction of bottom dross, (3) control the concentration of free Fe and free Al and the temperature, and (4) make sure the proper distribution of Fe, Al, and Fe_2Al_5 during the transition from manufacturing GA to manufacturing GI.