Masuzo Ueda1, Fumio Seki1 and Kazuo Hosokawa1
1Department of Mechanical engineering, Faculty of Technology, Kanazawa University, Kanazawa
Effects of the zinc or tin layer in hot dipped lead coating on galvanized or tinned steel were studied. The results obtained are sammarized as follows:
(1) The adhesiveness of lead coating is related to the dipping temperature and the thickness of the layer; the dipping temperature above 419°C is known to be necessary for the coating on galvanized steel. The length of dipping time is determined from the thickness of the layer.
(2) The optimum dipping temperature and dipping time are; (A) an ordinary dipping temperature at 360°C, more than 40 min for galvanized steel on account of exfoliation of the zinc layer in the early stage of dipping and more than 30 sec for tinned steel. (B) at 430°C, the one 3 min, the other above 30 sec. However, the excessive dipping time and temperature which give rise to oxidation of the specimens must be avoided.
(3) The zinc or tin layer on steel is not covered with molten lead, but the steel is coated with the intermediate alloy of the molten layer and lead. Therefore, the adhesion of lead coating is not proportional to the thickness of the layer.
(4) The adhesion of lead coating is increased remarkably by dipping after immersing in a concentrated hydrochloric acid for a few seconds. This is the reason why the specimens are cleaned by HCl, and SnCl2 or ZnCl2 is formed when zinc or tin dissolves in HCl.
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