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Hot Dip Galvanizing Process And Related Instructions

- Jul 25, 2018 -

Hot dip galvanizing process and related instructions

1. During the process, the workpiece should be degreased, washed with water, washed with acid, washed with water, immersed with plating solvent, dried and preheated with hot galvanizing, cleaned, cooled, passivated, rinsed and dried.

2. Process description

(1) degreasing can be done by chemical degreasing or water-base metal degreasing cleaning agent, until the workpiece is completely soaked by water.

(2) the pickling

Can use H2S04 15%, 0.1% thiourea, 40 ~ 60 ℃ or with 20% HC1, methenamine 3 ~ 5 g/L, 20 ~ 40 ℃ for pickling.Corrosion inhibitor can prevent overcorrosion and reduce hydrogen absorption of iron matrix.Aerosol inhibits acid mist escaping.

Poor degreasing and pickling treatment will result in poor adhesion of the plating layer and no zinc or zinc coating peeling off.

(3) immersion plating aid

Also known as solvent, can keep the before immersion plating workpiece has a certain active avoid secondary oxidation, coating and the magnesium substrate to enhance combining NH4C1 100-150 - g/L, ZnC12 150-180 - g/L, 70 ~ 80 ℃, 1 ~ 2 min.And add a certain amount of anti-explosion agent.

(4) drying and preheating

In order to prevent the workpiece deformation due to temperature rise sharply when dip, and remove the residual moisture, prevent to produce, zinc, zinc liquid splashes, caused by preheating shall generally be 80 ~ 140 ℃.

(5) hot galvanizing.

The temperature of the zinc solution, the dip time and the speed of the workpiece from the zinc solution should be controlled.The extraction speed is generally 1.5 m /mine

The temperature is too low, the zinc liquid has poor fluidity, and the coating is thick and uneven.Temperature: high, good fluidity of zinc liquid, easy to detach from workpiece, reduce the occurrence of flow hanging and wrinkling, strong adhesion, thin coating, good appearance and high production efficiency;However, the temperature is too high, and the iron loss of the workpiece and the zinc pot is serious, resulting in a large amount of zinc slag, which affects the quality of the zinc-impregnated layer and is easy to cause color difference, making the surface color ugly and zinc consumption high.

The thickness of the zinc layer depends on the temperature of the zinc solution, the time of zinc immersion, the steel material and the zinc liquid composition.

General factory in order to prevent the high temperature deformation and reduce zinc slag due to iron losses, is 450 ~ 470 ℃, 0.5 ~ 1.5 min.Some factories use high temperature for large parts and cast iron parts, but avoid the temperature range of the peak iron loss.But we suggest that the added in the liquid zinc iron function and reduce the eutectic temperature of the alloy and galvanized temperature drops to 435-445 ℃.

(6) to sort out

After plating, the finishing of the workpiece is mainly to remove the residual zinc and zinc tumor on the surface.

(7) passivation

The purpose is to improve the anti-atmospheric corrosion performance of workpiece surface, reduce or prolong the appearance time of white rust, and keep the coating with good appearance.All were passivated with chromate, such as Na2Cr207 80~100g/L, and sulfuric acid 3~4ml/L. However, this passivator seriously affected the environment, and it was best to use chrome-free passivation.

(8) cooling

Generally with water, but not too low nor too high temperature, is generally not less than 30 ℃ is not higher than 70 ℃,

(9) test"

The appearance of the coating is bright, meticulous, no flow hanging, wrinkling phenomenon.Coating thickness gauge can be used for thickness test.The coating thickness can also be obtained by the conversion of zinc attachment.The combined strength can be bent by bending press. The sample should be bent 90~180", and no cracks or coating should be lost.It can also be tested by hammering and salt spray test and copper sulfate etching test in batches.