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Why does the production of packaging steel strips form spangles of different sizes
by：Hongmei
2021-03-15
Why does the production of packaging steel strips form spangles of different sizes
During normal solidification, if no spangle promoting elements are added to the galvanizing solution, the coating is cooled and crystallized in a spontaneous state, and a large number of crystal nuclei can be formed to grow into extremely small spangles. It is almost invisible to the naked eye, like there is no spangle, so it is called spangle-free product.
If zinc flower promoting elements such as lead and antimony are added to the zinc plating solution, they will hinder the formation of crystal nuclei, and only a small amount of embryos can grow into crystal nuclei, so the final crystal grain is larger, that is, zinc The flower is larger, which is the big spangle product. When the large spangles are crystallized, lead or antimony will be repelled to the grain boundaries, blackening will occur after long-term use, and oxidation and corrosion will begin at the grain boundaries. Therefore, although the large spangles are beautiful in appearance, they are 'not useful' and the corrosion resistance is affected. As early as the 1970s, the large spangles products were eliminated in foreign countries.
If spangle promoting elements are added to the galvanizing solution, a large number of crystal nuclei can be formed under the action of external forces, so that the size of the spangle after crystallization is smaller, and a small spangle product is formed . The common small spangle production processes are:
(1) Spray water on the unsolidified coating to cool the coating quickly, thereby forming a large number of crystal nuclei.
(2) Spray zinc powder on the surface of the unsolidified coating. These zinc powders can become foreign crystal nuclei, and the zinc solution can crystallize and grow into smaller spangles on these zinc powders.
(3) Ammonia gas is introduced at the end of the annealing furnace to condense the ammonia gas on the surface of the steel strip to form extremely small particles. These particles will also become foreign nuclei during crystallization, on which the crystals will grow up. Small spangles.
During normal solidification, if no spangle promoting elements are added to the galvanizing solution, the coating is cooled and crystallized in a spontaneous state, and a large number of crystal nuclei can be formed to grow into extremely small spangles. It is almost invisible to the naked eye, like there is no spangle, so it is called spangle-free product.
If zinc flower promoting elements such as lead and antimony are added to the zinc plating solution, they will hinder the formation of crystal nuclei, and only a small amount of embryos can grow into crystal nuclei, so the final crystal grain is larger, that is, zinc The flower is larger, which is the big spangle product. When the large spangles are crystallized, lead or antimony will be repelled to the grain boundaries, blackening will occur after long-term use, and oxidation and corrosion will begin at the grain boundaries. Therefore, although the large spangles are beautiful in appearance, they are 'not useful' and the corrosion resistance is affected. As early as the 1970s, the large spangles products were eliminated in foreign countries.
If spangle promoting elements are added to the galvanizing solution, a large number of crystal nuclei can be formed under the action of external forces, so that the size of the spangle after crystallization is smaller, and a small spangle product is formed . The common small spangle production processes are:
(1) Spray water on the unsolidified coating to cool the coating quickly, thereby forming a large number of crystal nuclei.
(2) Spray zinc powder on the surface of the unsolidified coating. These zinc powders can become foreign crystal nuclei, and the zinc solution can crystallize and grow into smaller spangles on these zinc powders.
(3) Ammonia gas is introduced at the end of the annealing furnace to condense the ammonia gas on the surface of the steel strip to form extremely small particles. These particles will also become foreign nuclei during crystallization, on which the crystals will grow up. Small spangles.
