Hot-dip galvanizing is one of the effective methods to improve the resistance of steel grating to atmospheric corrosion. It is widely used because of its excellent coating performance, long service life, and basically no maintenance as a protective layer. The surface of the hot-dip galvanized layer of steel grating has many common quality defects, such as missing plating, striped feather white patterns, ultra-thick, rough, Darkness, tear streaks, turtle cracks, crystal-like raised lines, "white rust", etc. There are many influencing factors and it is relatively difficult to control. In this regard, we can start by strengthening process control, supplemented by necessary process measures, to improve the surface quality of hot-dip galvanized steel grating. The following analyzes the causes and control methods of surface defects in the hot-dip galvanized layer of steel gratings:
1. Surface pretreatment
Poor surface pretreatment of steel gratings is the main reason for missing plating (iron exposure). Steel gratings are inevitably stained with paint or mineral grease during the process of leaving the factory, storage, transportation, and processing. Sometimes the flaw detection surface of the welding part needs to be coated with special grease that is difficult to clean. Most companies do not have a degreasing process and only rely on pickling to remove surface impurities, which can easily cause missing plating (iron exposure). Another situation is that the pickling steel gratings are relatively concentrated, densely stacked, and heavy during the pickling process, resulting in under-pickling and line clamping, or the pickling concentration is too high, causing acid salts to precipitate on the surface and grooves. In the tank, if the water is not washed or the water is not washed thoroughly, it is easy to cause leakage and virtual plating. Furthermore, due to the aging and failure of the solvent, and the steel grating is not opened in time during the drying process, or the drying time If it is too long, secondary micro-oxidation will occur on the surface of the steel parts and acidic iron salts will be formed to cover the surface, which will also easily lead to missed plating. It is especially common in climates with high relative humidity and foggy weather, and this situation is often easily overlooked. In addition, when using solvent hot-dip galvanizing, if the ratio of the most commonly used mixed aqueous solution of ZnCl2 and NH4Cl is incorrect, no eutectic point will be formed. Especially when the concentration is too high, ash inclusion leakage can easily occur in the welding corner joints of steel gratings.
2. The thickness of the galvanized layer is not enough
If the thickness of the galvanized layer of the steel grating does not meet the standard requirements, it will directly affect the service life of the product. The reasons for the insufficient thickness of the galvanized layer of the steel grating are as follows.
(1) Influence of zinc liquid temperature. When the temperature of the zinc liquid is lower than 430 degrees, the zinc-iron diffusion rate is low, and it is difficult to generate a sufficient iron-zinc alloy layer, and the entire coating is thin. When the temperature is 460 degrees, the zinc layer thickens. When the temperature continues to rise, the zinc liquid The zinc layer becomes thinner and the zinc layer becomes thinner, so the temperature of the zinc liquid must be strictly controlled to ensure the stability of the quality of the steel grating.
(2) The influence of the residence time of the steel grating in the zinc liquid. The residence time of the steel grating in the zinc liquid has a certain time range, which is determined according to the thickness of the steel grating. As the galvanizing time is extended, the thickness of the coating will increase, but excessively extending the galvanizing time will make the zinc layer brittle, which will affect the quality.
(3) The influence of the method of extracting the steel grating from the zinc liquid. When the steel grating is led out of the zinc liquid, it should be led out vertically. When the steel grating is led out at an angle, the zinc layer will be thin. Therefore, the steel grating should be led out vertically when led out of the zinc pot.
The above is the analysis of surface defects of hot-dip galvanized steel grating introduced by the editor. I hope it can help you. If you want to know anything else, you can contact us.
