Zinc flowers
Reduce the zinc liquid. Solidification temperature By extending the growth time of zinc flower crystals, the molten zinc on the surface of the galvanized strip steel forms zinc flowers. High-purity zinc cannot form zinc flowers because it lacks crystallization nuclei. Heat Galvanized steel sheet The surface features beautiful zinc flowers, which is one of its most distinctive characteristics that sets it apart from other coated sheets.
Types of zinc flowers
(1) Large Zinc Flowers
Zinc blooms with a diameter greater than 3 mm that can be distinguished with the naked eye are referred to as large zinc blooms; some also call them normal or natural zinc blooms. The internationally recognized optimal size is between 8 and 12 mm.
In nature, lead and zinc often occur together in symbiotic ore deposits. When smelted using pyrometallurgical processes, the lead melt—being denser—settles at the bottom, while the zinc melt—being less dense—rises to the top, allowing for their separation. However, the saturation concentration of lead in the zinc melt is only 2%; thus, crude zinc contains substantial amounts of lead. Hot-dip galvanizing has a history of over 150 years. At that time, there were no modern refining technologies available, so only crude zinc was used for hot-dip galvanizing. Because lead was inevitably mixed into the zinc melt, zinc blooms were bound to appear on hot-dip galvanized sheets. As a result, for a long time, it became widely believed—and erroneously—that hot-dip galvanized sheets must have zinc blooms; without them, a sheet could not be considered hot-dip galvanized. In reality, having zinc blooms on hot-dip galvanized sheets offers no real benefits. First, the presence of lead or antimony in the zinc coating can accelerate...
Electrochemical corrosion First, higher speeds can reduce the service life of hot-dip galvanized sheets by 15% to 20%. Second, the presence of zinc flowers can result in an uneven surface. Third, zinc flowers are detrimental to subsequent coating processes, as each zinc flower tends to leave behind a dark spot, thereby compromising the aesthetic appeal. Currently, developed countries in Europe and the U.S. no longer produce hot-dip galvanized sheets with large zinc flowers; they have all shifted toward products without zinc flowers. Only in less-developed countries in Southeast Asia do large-zinc-flower varieties still remain in use.
(2) Small Zinc Flowers
Zinc flowers with a diameter of 1–2 mm are referred to as "small zinc flowers." After hot-dip galvanized sheets exit the zinc bath, if a mist of water or zinc powder is sprayed onto the still-liquid zinc layer, each droplet of water mist or particle of zinc powder will serve as a crystallization nucleus, thereby increasing the number of zinc flowers per unit area while reducing their size. As a result, the surface of the galvanized sheet develops small zinc flowers that can be distinguished by the naked eye. Traditionally, products manufactured using this process are called "small zinc flower" galvanized sheets. However, since this process often leads to uneven zinc flower distribution and inconsistent surface coloration, and because it incurs high production costs, it is now rarely used.
(3) No zinc bloom
The zinc bloom is invisible to the naked eye on the surface, and such a product is referred to as “zinc-bloom-free” or “zero-zinc-bloom.” This is achieved by precisely controlling the chemical composition of the zinc bath. During hot-dip galvanizing, only a specific amount of aluminum is added to the zinc bath—without adding lead, antimony, or tin—to produce zinc-bloom-free products. This process requires no additional equipment and incurs no extra production costs, yet it delivers a uniformly consistent surface appearance. As a result, this technology has been widely adopted and promoted around the world.
(4) Bright Zinc Flowers
Large zinc blooms are not permitted to enter the finishing process. Products with small zinc blooms or no zinc blooms, after being processed through the finishing step, are referred to as finished zinc blooms.
