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What are the effects of contaminants on the surface of the packaging steel strip on hot-dip galvanizing?
by：Hongmei
2021-03-15
What are the effects of contaminants on the surface of the packaging steel strip on the hot dip galvanizing?
If there is pure cold rolling oil on the surface of the steel strip, its volatilization temperature is about 180℃, which can basically be vaporized in the galvanizing annealing furnace, participating in the combustion of the anaerobic furnace or exhausting the furnace gas with the furnace. So the impact is not big. However, cold emulsifiable concentrates are often mixed with lubricating grease, iron powder, and dust to form highly viscous oil stains, which firmly adhere to the steel belt. Therefore, to remove solid contaminants, it must first be degreased.
Lubricating grease appears on the surface of the steel strip as a grease spot, which is difficult to clean and remove. A small amount of lubricating oil can also volatilize in the furnace, but the lubricating oil often contaminates the steel strip in pieces, so it is not It may be completely volatilized. It increases the surface tension of the steel strip during galvanizing, affects the wettability of the zinc liquid and the steel strip, separates the steel strip from the zinc liquid, and causes defects such as steel exposure and poor galvanizing, and makes the product scrapped.
The iron powder on the surface of the steel strip is very harmful to the galvanizing process. Under the high temperature in the furnace, it will adhere to the furnace bottom roller, forming furnace bottom roller nodules. When the furnace bottom roller and the steel belt move relative to each other, it will cause scratches. It will react with the zinc liquid in the zinc pot to form zinc lynx. Zinc slag is composed of more zinc and less iron. 1kg of iron powder can form 8kg of zinc slag, and then absorb a certain amount of zinc liquid, so a very small amount of iron powder will have a great impact. Some of these zinc slags enter the zinc pot to form bottom dross and scum, and most of them adhere to the surface of the steel strip to form defects such as zinc particles, zinc slag, and zinc scars, which seriously affect the performance and appearance of the product. The iron powder adheres to the stabilizer roller and the sinking roller in the zinc pot, and the lack of filling of the sticky slag on the surface of the roller will cause imprinting on the surface of the steel strip, which is the main reason for the downtime to change the roller.
The dust on the surface of the steel strip and the alkali stains left over after degreasing will become the core of a crystal when the zinc liquid solidifies, and a dust particle or alkali stain will form a crystalline core, forming a pattern. Therefore, there are many crystal cores in areas with dense dust or alkali stains, which solidify before the clean place. The number of spangles is large. The growth of spangles is restricted and becomes uneven small spangles. This not only affects the uniformity of spangles, but also More importantly, it affects the bonding force between the zinc layer and the substrate, causing the plating layer to fall off during use.
Therefore, pre-treatment is the first critical process in the galvanizing line that affects product quality. It uses physical and chemical methods to remove most of the grease, iron powder, dust and other pollutants on the surface of the steel strip. It can also partially remove contaminants with strong adhesion such as rust. This is one of the most basic tasks before galvanizing. As long as the pre-treatment is passed, the galvanizing is half done. People pay more and more attention to the importance of pre-treatment. The improved Sendzimir production line designed in the early days has a strong purging and degreasing effect on the steel strip due to the anaerobic furnace. There is no pre-treatment designed, but it has been carried out in recent years. Transformation, adding pre-treatment procedures. No matter what kind of process method is adopted in the currently designed production line, pre-treatment is designed, and the process route is getting longer and longer, the process is getting more and more advanced, the effect is getting better and better, and the investment is increasing.
If there is pure cold rolling oil on the surface of the steel strip, its volatilization temperature is about 180℃, which can basically be vaporized in the galvanizing annealing furnace, participating in the combustion of the anaerobic furnace or exhausting the furnace gas with the furnace. So the impact is not big. However, cold emulsifiable concentrates are often mixed with lubricating grease, iron powder, and dust to form highly viscous oil stains, which firmly adhere to the steel belt. Therefore, to remove solid contaminants, it must first be degreased.
Lubricating grease appears on the surface of the steel strip as a grease spot, which is difficult to clean and remove. A small amount of lubricating oil can also volatilize in the furnace, but the lubricating oil often contaminates the steel strip in pieces, so it is not It may be completely volatilized. It increases the surface tension of the steel strip during galvanizing, affects the wettability of the zinc liquid and the steel strip, separates the steel strip from the zinc liquid, and causes defects such as steel exposure and poor galvanizing, and makes the product scrapped.
The iron powder on the surface of the steel strip is very harmful to the galvanizing process. Under the high temperature in the furnace, it will adhere to the furnace bottom roller, forming furnace bottom roller nodules. When the furnace bottom roller and the steel belt move relative to each other, it will cause scratches. It will react with the zinc liquid in the zinc pot to form zinc lynx. Zinc slag is composed of more zinc and less iron. 1kg of iron powder can form 8kg of zinc slag, and then absorb a certain amount of zinc liquid, so a very small amount of iron powder will have a great impact. Some of these zinc slags enter the zinc pot to form bottom dross and scum, and most of them adhere to the surface of the steel strip to form defects such as zinc particles, zinc slag, and zinc scars, which seriously affect the performance and appearance of the product. The iron powder adheres to the stabilizer roller and the sinking roller in the zinc pot, and the lack of filling of the sticky slag on the surface of the roller will cause imprinting on the surface of the steel strip, which is the main reason for the downtime to change the roller.
The dust on the surface of the steel strip and the alkali stains left over after degreasing will become the core of a crystal when the zinc liquid solidifies, and a dust particle or alkali stain will form a crystalline core, forming a pattern. Therefore, there are many crystal cores in areas with dense dust or alkali stains, which solidify before the clean place. The number of spangles is large. The growth of spangles is restricted and becomes uneven small spangles. This not only affects the uniformity of spangles, but also More importantly, it affects the bonding force between the zinc layer and the substrate, causing the plating layer to fall off during use.
Therefore, pre-treatment is the first critical process in the galvanizing line that affects product quality. It uses physical and chemical methods to remove most of the grease, iron powder, dust and other pollutants on the surface of the steel strip. It can also partially remove contaminants with strong adhesion such as rust. This is one of the most basic tasks before galvanizing. As long as the pre-treatment is passed, the galvanizing is half done. People pay more and more attention to the importance of pre-treatment. The improved Sendzimir production line designed in the early days has a strong purging and degreasing effect on the steel strip due to the anaerobic furnace. There is no pre-treatment designed, but it has been carried out in recent years. Transformation, adding pre-treatment procedures. No matter what kind of process method is adopted in the currently designed production line, pre-treatment is designed, and the process route is getting longer and longer, the process is getting more and more advanced, the effect is getting better and better, and the investment is increasing.
