Method of Forming Electric Insulating Films on Al-Containing Silicon Steel Sheet and Surface-Coated Al-Containing Silicon Steel Sheet

摘要

1,183,092. Coated steel sheet. YAWATA IRON & STEEL CO. Ltd. 14 March, 1967 [18 March, 1966], No. 11813/67. Heading B2K. [Also in Division C7] In a process for annealing an aluminium containing silicon steel sheet (e.g, containing 0.01-0.09% soluble Al) the annealing separator comprises a coating of a Mg compound and one or more compounds of Mn, Cu, Cr or Zn which has been applied as a solution or suspension thereof. During the annealing in a high temperature reducing atmosphere, the above compounds and Al 2 O 3 in the surface of the steel sheet form a glassy electrically insulating film. The ratio of Mg compound to other compound (calculated as the monoxide) is preferably 98:2 to 20:80. The coating may be applied by roller, spraying or dipping of a mixed solution of the required compounds or the Mn compound may be applied as a first layer and the Mg as a second layer. Alternatively one of the layers in a two layer process may be applied by electrolysis. The coated sheet may be given a further coating by applying, drying and baking a coating using a solution prepared by adding at least one of water glass, MgO, CaO, ZnO and silicic anhydride, to a solution containing H 3 PO 4 5-40 wt. %. CrSP6+/SP compound 1-10 wt. % #boric acid or a borate #less than 8 wt. % alternatively a solution of 1-6 wt. % zinc dichromate with 1-4% glycerine and 2-5% boric acid may be used. Where the sheet does not need to be stress-relief annealed an organic, or mixed organic/inorganic, film may be applied to the coated sheet.