METHOD OF FORMING ELECTRIC INSULATING COATING ON THE SURFACE OF SILICON STEEL SHEET WITH SERPENTINE

摘要

A method of treating silicon steel sheet and forming an electric insulating coating having excellent adherent, heat resisting and electric insulating properties on the surface of a silicon steel sheet is disclosed comprising the steps of coating the surface of a silicon steel sheet containing 2 to 4 percent by weight of silicon with a separator formed from an aqueous slurry state consisting of 5 to 40 percent by weight of serpentine material and the remainder of magnesia to which may be added 4 to 40 percent by weight of manganous oxide powder, the coating will include the serpentine material in its dried state to an amount of 0.5 g/m2 to 6.0 g/m2, the magnesia in its dried state to an amount of 2 g/m2 to 12 g/m2 and the manganous oxide, if present, in its dried state in an amount of 0.5 g/m2 to 6.0 g/m2, the coating step is followed by drying the silicon steel sheet thus coated, and box annealing the coated and dried steel sheet in a reducing atmosphere containing hydrogen at a high temperature.