Hot-dip galvanizing is one of the important anti-corrosion methods commonly used for surface treatment of steel grating. In a corrosive environment, the thickness of the galvanized layer of the steel grating has a direct impact on corrosion resistance. Under the same bonding strength conditions, the thickness of the coating (adhesion amount) is different, and the corrosion resistance period is also different. Zinc has extremely excellent performance as a protective material for the steel grating base. The electrode potential of zinc is lower than that of iron. In the presence of electrolyte, zinc becomes an anode and loses electrons and corrodes preferentially, while the steel grating base becomes a cathode. It is protected from corrosion by the electrochemical protection of the galvanized layer. Obviously, the thinner the coating, the shorter the corrosion resistance period, and the corrosion resistance period increases as the coating thickness increases. However, if the coating thickness is too thick, the bonding strength between the coating and the metal substrate will drop sharply, which will reduce the corrosion resistance period and is not economically cost-effective. Therefore, there is an optimal value for the coating thickness, and it is not good to be too thick. After analysis, for hot-dip galvanized steel grating plating parts of different specifications, the optimal coating thickness is most suitable to achieve the longest corrosion resistance period.
Ways to improve coating thickness
1. Choose the best galvanizing temperature
How to control the galvanizing temperature of steel grating is very important to ensure and improve the coating quality. After years of production practice, we believe that it is ideal to control the hot-dip galvanizing temperature at 470~480℃. When the thickness of the plated part is 5mm, the coating thickness is 90~95um (ambient temperature is 21~25(). At this time, the hot-dip galvanized steel grating is tested by the copper sulfate method. The results show that: the coating is immersed for more than 7 times without exposing the iron matrix; the galvanized flat steel is bent (90 degrees) for more than 1 time without the coating falling off. When the zinc immersion temperature is 455~460℃, the coating thickness has exceeded the optimal value. At this time, although the coating uniformity test results are good (usually immersed for more than 8 times without exposing the matrix), due to the increase in zinc liquid viscosity, the sagging phenomenon is more obvious, the bending test is not guaranteed, and even defects such as delamination occur. When the zinc immersion temperature is 510~520℃, the coating thickness is less than the optimal value (usually less than 60um). The maximum number of uniformity measurements is 4 immersions to expose the matrix, and the corrosion resistance is not guaranteed.
2. Control the lifting speed of the plated parts. The speed of lifting the steel grating plated parts from the zinc liquid has an important influence on the coating thickness. When the lifting speed is fast, then The galvanized layer is thick. If the lifting speed is slow, the coating will be thin. Therefore, the lifting speed should be appropriate. If it is too slow, the iron-zinc alloy layer and the pure zinc layer will diffuse during the lifting process of the steel grating plated parts, so that the pure zinc layer is almost completely transformed into an alloy layer, and a gray-thirsty film is formed, which reduces the bending performance of the coating. In addition, in addition to being related to the lifting speed, it is also closely related to the lifting angle.
3. Strictly control the zinc immersion time
It is well known that the thickness of the steel grating coating is directly related to the zinc immersion time. The zinc immersion time mainly includes the time required to remove the plating aid on the surface of the plated parts and the time required to heat the plated parts to the zinc liquid temperature and remove the zinc ash on the liquid surface after zinc immersion. Under normal circumstances, the zinc immersion time of the plated parts is controlled to the sum of the time when the reaction between the plated parts and the zinc liquid is terminated and the zinc ash on the liquid surface is removed. If the time is too short, the quality of the steel grating plated parts cannot be guaranteed. If the time is too long, the thickness and brittleness of the coating will increase, and the corrosion resistance of the coating will be reduced, which will affect the service life of the steel grating plated parts.
Post time: Jun-20-2024