1.What is the effect of air knife parameters on zinc layer uniformity?
Problem: Inconsistent pressure, distance, and angle of the air knife (the device controlling zinc layer thickness) can lead to uneven zinc layer thickness in the transverse direction. Areas with thicker zinc layers cool more slowly, resulting in larger, brighter zinc blooms; areas with thinner zinc layers cool more quickly, producing smaller blooms and a relatively darker or grayish color.
Adjustment Method:
Optimize the air knife parameters to ensure uniform zinc layer thickness across the strip width.
Regularly inspect and clean the air knife nozzle to prevent clogging.
2.What are the effects of zinc bath composition and temperature?
Aluminum Content: During pure zinc plating, unstable aluminum content in the zinc bath affects the formation of zinc spangles and surface gloss. Excessive aluminum content inhibits spangle growth, resulting in spangle-free or small spangle surfaces with a bluish-white color.
Alloying Elements: Elements such as lead, antimony, and bismuth are traditionally used to promote the formation of large zinc spangles, but their segregation can lead to uneven spangle size and alternating light and dark color variations.
Temperature: Fluctuations in the zinc bath temperature affect the fluidity and solidification rate of zinc, resulting in inconsistent surface conditions.
Adjustment Methods:
Strictly control the composition of each element in the zinc bath within the target range, especially the aluminum content.
In modern production lines, low-lead or lead-free formulations are preferred, along with other technologies (such as micro-spraying) to control surface morphology, thereby obtaining a more uniform surface with small or no zinc spangles.
Maintain a stable zinc bath temperature.
3.What impact do cooling conditions have?
Problem: The cooling rate and uniformity of the strip steel after exiting the zinc bath are crucial. Uneven cooling directly leads to uneven zinc flower size, which is the most common type of color difference. Areas with faster cooling have smaller, darker zinc flowers; areas with slower cooling have larger, brighter zinc flowers.
Adjustment Method:
Ensure that the cooling systems, including air cooling and water cooling, are in good working order, and that airflow direction, speed, and water volume are evenly distributed.
Optimize the cooling process according to the specifications and speed of the steel coil.
4.What impact does the condition of the galvanizing line equipment have?
Problem:
Stabilizing Rolls: If zinc dross adheres to the surface of the stabilizing rolls or if they are not perfectly round, it will scratch the incompletely solidified zinc layer, forming roll marks that appear as regular stripe-like or dotted color differences.
Submerged Rolls, Correction Rolls: The condition of the surfaces of these rolls also affects the flatness of the strip surface, indirectly causing color differences.
Adjustment Method:
Regularly clean and maintain all rolls that come into contact with the strip to ensure their surfaces are smooth and flat.
5.What are the effects of surface treatment?
Problem:
Passivation Treatment: Uneven application of the passivation solution, fluctuations in concentration, or incomplete drying can lead to passivation films of varying colors and thicknesses on the strip surface. For example, colorless passivation may exhibit interference color differences due to uneven film thickness; colored passivation (such as blue-white or multicolored) directly manifests as uneven color.
Oil Coating: Uneven oil film thickness can form oil spots on the surface, which appear as color differences due to light interference.
Adjustment Methods:
Ensure the nozzles of the passivation solution/oil coating system are unobstructed and the pressure is stable.
Roller coating is generally more uniform than spraying.
Strictly control the drying temperature and time to ensure complete curing of the passivation film.