MATERIAL AND METHOD FOR TESTING HYGROSCOPICITY OF INSULATION FILM OF STEEL MATERIAL

摘要

PURPOSE:To enable quick and simple quantitative evaluation of hygroscopicity of a phosphate insulation film applied on a steel material, by using a sheet of test material which is made to support a solution containing an inhibitor for Mo acid ion and Fe. CONSTITUTION:A sheet of test material which is made to support a solution containing 0.1-20wt.% of an inhibitor for Mo acid ion and Fe is press-fitted on a surface to be inspected of an electric iron plate having a phosphate insula tion film. Phosphoric acid eluted from the insulation film reacts with Mo acid in the sheet of test material and forms a sediment of phosphomolybdeic acid, turning yellow. Moreover, if the sheet of test material is treated by a solution containing a reducing agent, a hygroscopic part of the film can be discriminate as blue spot. This enables quick quantitative evaluation of the hygroscopicity of the phosphate insulation film of a steel material such as electric iron plate.