Steel surface treatment rust removal grade standards

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As the saying goes, “30% is the paint, 70% is the application process,” and in this process, the quality of surface treatment of the material is of utmost importance. Relevant studies show that the quality of surface treatment accounts for 40-50% of the factors affecting the quality of the coating. The role of surface treatment in coating is self-evident. Rust removal grade: Refers to the level of cleanliness achieved in surface treatment. The national standard GB8923-2011 for steel surface treatment provides a description of rust removal grades【1】. Jet or blast rust removal is denoted by the letter “Sa”. There are four rust removal grades: Sa1 for mild blasting or jetting – without magnification, the surface should be free of visible grease and dirt, as well as any loosely attached oxides, rust, paint coatings, and other contaminants. With thorough spraying or blasting for rust removal using Sa2, the surface should be free of visible grease and dirt when viewed without magnification; there should be almost no scale, rust, coatings, or foreign contaminants, and any remaining residues should be firmly attached. With Sa2.5-level thorough jetting or blasting for rust removal, the surface, when viewed without magnification, should be free of visible oils, dirt, scale, rust, coatings, and foreign contaminants; any remaining traces of such contaminants should appear only as slight spot-like or streaky discolorations. For Sa3 steel, spray or shot blasting to achieve a clean surface finish means that, without magnification, there should be no visible oil, grease, dirt, scale, rust, coatings, or foreign contaminants on the surface; the surface should have a uniform metallic color. 【2】Rust removal using manual and power tools is indicated by the letter “St”. There are two rust removal grades: St2 requires thorough manual and power tool rust removal; without the use of magnification, the surface should be free of visible oil, grease, and dirt, as well as any loosely attached scale, rust, coatings, or foreign contaminants. St3 is the same as St2, but more thorough; the surface should have the luster of the base metal. 【3】During flame cleaning, without magnification, the surface should be free of visible oil, grease, dirt, scale, rust, coatings, and foreign contaminants; any remaining traces should be limited to surface discoloration.