Preparation method for chromium-free environment-friendly conversion coating before plastic dipping of galvanized steel pipe

Abstract

The invention discloses a preparation method for a chromium-free environment-friendly conversion coating before plastic dipping of a galvanized steel pipe. The preparation method comprises the following steps: 1) acidic degreasing; 2) washing; 3) washing; 4) chromium-free conversion: taking inorganic auxiliaries, complexing agent, pH regulator, rare-earth salts and silane as raw materials in a chromium-free conversion solution, taking an organic acid as a cross-linking accelerant for chemical conversion coating, combining silane solution with rare-earth salts and compounding with the surface of the galvanized steel pipe so as to form a film, wherein PH value is 2.5-4.0, temperature is at 25-40 DEG C and time is 3-5 min; 5) washing; 6) pre-drying; 7) plastic dipping: fluidizing; 8) levelingcuring. Compared with the prior art, the preparation method for the chromium-free environment-friendly conversion coating before the plastic dipping of the galvanized steel pipe, disclosed by the invention, has the beneficial effects that the decay resistance of the conversion coating is excellent, the treatment of wastewater is further reduced and the conversion coating is chromium-free and environment-friendly.

Description

Technical field [0001] The invention relates to a method for preparing a conversion film of a galvanized steel pipe, in particular to a method for preparing a chromium-free environmental protection conversion film before the galvanized steel pipe is dipped. Background technique [0002] Dipping: refers to the process of coating plastic powder on the metal surface after heating to achieve corrosion resistance. [0003] Dipping is a heating process, metal is preheated, dipped, and solidified. During immersion, the heated metal sticks to the surrounding materials. The hotter the metal, the longer the immersion time and the thicker the material. Naturally, the temperature and the shape of the dipping material are the key to determining how much the plastisol sticks. Amazing shapes can be made by dipping. Hot-dip plastic powder raw materials: PE general-purpose dipping powder, PE engineering dipping powder, PE pipe-type dipping powder Conversion film: Conversion film is the metal pro...

AI Technical Summary

Problems solved by technology

[0004] In the prior art, there are the following technical problems: 1. If the hot-dip galvanized layer is not treated, its corrosion resistance is poor, and black spots or white rust are easily generated in the environment, and the anti-corrosion effect is greatly reduced. Furthermore, the galvanized steel pipe The adhesion between itself and the dipping PE powder is extremely poor, and the interface between the PE coating and the workpiece is easily corroded by the medium, thus forming voids or corrosion products, resulting in coating peeling off; 2. Chromate passivation is simple in process and low in cost , has the advantage of good anti-corrosion effect on the galvanized layer, and is widely used in many fields, but hexavalent chromium is highly toxic and carcinogenic, and poses serious harm to the human body and the environment

Images