3、 Treatment before metal coating (1) structural treatment of sharp corners, splashes, welding slag, welding holes, etc., chamfering treatment to reduce stress concentration, etc. (2) The surface shall be cleaned of oxide scale (rolling), rust, soluble salt, grease, insoluble solids, moisture (excluding water-based paint), etc. (3) The surface roughness improves the roughness and increases the mechanical engagement between the coating and the substrate. If the roughness is too large, the convex part may cause the local coating to be too thin, and the residual bubbles in the pits will lead to premature failure of the coating. Generally, the roughness should be 1/10 of the coating thickness.
4、 Ideal surface pretreatment effect: (1) no grease (water-based coating is more important), no rust products (sometimes cannot be identified by naked eyes), and no dirt; (2) Substrate surface with certain roughness; (3) Add a layer of chemical conversion film (such as phosphating film, coupling agent, phytate film, etc.) and transition layer (aluminum alloy profile anodic oxidation film, etc.).
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