Chrome-free passivating agent for hot galvanizing structural part and preparation method thereof

Abstract

The invention relates to a chrome-free passivating agent for a hot galvanizing structural part. The chrome-free passivating agent for the hot galvanizing structural part is prepared from the followingraw materials in parts by weight: 10 to 20 parts of molybdate, 10 to 15 parts of phytic acid, 8 to 12 parts of glutinous rice flour, 2 to 4 parts of a cross-linking agent, 5 to 10 parts of water dispersible nano-silica, 2 to 4 parts of a dispersing agent and 46 to 63 parts of water, wherein the pH of the chrome-free passivating agent is 4.5 to 5.5; a preparation method of the chrome-free passivating agent for the hot galvanizing structural part comprises the following steps: after the glutinous rice flour is enabled to pass through a 200-mesh sieve, weighing various raw materials by weight, adding the phytic acid, the molybdate and the cross-linking agent into the water first, stirring uniformly, adding the glutinous rice flour, heating to 60 to 70 DEG C, stirring until the glutinous riceflour is dissolved, adding the dispersing agent and the water dispersible nano-silica, then, stirring and dispersing uniformly at 60 to 70 DEG C, then regulating the pH to be 5.0, and cooling to obtain the chrome-free passivating agent for the hot galvanizing structural part. The chrome-free passivating agent for the hot galvanizing structural part is environment-friendly and chrome-free, and hashigh corrosion resistance.

Description

Technical field [0001] The invention belongs to the technical field of galvanizing, and specifically relates to a chromium-free passivator for hot-dip galvanizing structural parts and a preparation method thereof. Background technique [0002] Hot-dip galvanizing is the most commonly used protective cathodic protection method for cold-rolled steel sheets, but the galvanized layer is easily corroded in air (especially in humid air). In order to prevent the corrosion of the galvanized layer, a passivation treatment is required. The traditional passivation method is to coat the surface of the hot-dip galvanized steel sheet with a hexavalent chromium passivation agent, and form a passivation layer containing hexavalent chromium salt after drying. , But hexavalent chromium is toxic and carcinogenic, not only affecting human health, but also easily causing harm to the environment, and it will be gradually eliminated by the market. The ROHS directive issued by the European Union clearl...

AI Technical Summary

Problems solved by technology

[0003] Among the existing chromium-free passivators, molybdate is regarded as an alternative to chromate passivation treatment due to its low toxicity. Although it has been developed for several years, the neutral salt spray test has not been tested so far. It cannot be compared with the chromate passivation film. In addition, for some galvanized structural parts with many corners, the corners are easy to wear, so a thicker film layer and stronger adhesion are required. As the thickness of the molybdate passivation film increases, the adhesion becomes worse, and the film layer will appear cracks and cracks, so that the thickness of the molybdate film cannot be further broken through. Application on galvanized parts with many corners

Therefore, a kind of really satisfactory molybdate chromium-free passivator that can be used on hot-dip galvanized structural parts does not appear yet

Images