SURFACE

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Surface Pretreatment INCREASE FOR CORROSION PROTECTION

Někdy je samotná aplikace barev na očištěné a odmaštěné podklady nedostatečná z hlediska antikorozní ochrany a každé zvýšení této ochrany má značné ekonomické přínosy.


pretreatment in tetrafluorotitanic acid solution.
 

 

Chromating is effective for treating almost all metals, most often zinc and aluminum. By reacting the hexavalent chromium solution with the metal, the chromium is reduced, the metal surface oxidized, and the insoluble chromium-metal compound formed. Due to the toxicity of hexavalent chromium, it is replaced today by other methods, for example in the case of aluminum pretreatment, so-called titanation and also trivalent chromate.


 

Phosphating is used for steel, zinc and aluminum surfaces. Phosphating utilizes the ability of some metals (Fe, Zn, Mn) to form primary, secondary or tertiary phosphates of these metals in divalent form. There is only trivalent ferric phosphate, which is the least soluble of all. Phosphatization is effected by the action of phosphoric acid on the metal to form insoluble phosphates chemically bound to the crystal lattice of the metal. The chemical composition of the phosphatizing baths varies according to the metal to be treated. For successful phosphating it is necessary to maintain the prescribed temperature in the range of +/- (5 -8) ° C and concentration of the solution. The process of phosphating steel, whether ferric or zinc, would itself take place at 90 ° C for about 20-30 minutes, therefore it is accelerated by various oxidizing agents (nitrates, chlorates), which can reduce the time needed at 30-70 ° C immersion for 5-10 minutes, spraying for 1-3 minutes. The amount of excreted phosphate is in the range of 0.5-8.0 grams of phosphate per m², ie about 0.25-4.0 (micro) m. Higher layers can be brittle and cause poor paint adhesion for mechanically stressed products.