What is zero spangle steel?

Answer 1

The dictionary defines “spangle” as a glittering object. When spangle is used to define the surface appearance of galvanized steel sheet, it includes the typical snowflake-like or six-fold star pattern that is visible to the unaided eye. Non-Spangled Coatings In recent times, the production of zinc from zinc-containing ores has been changed to an electrolytic recovery method. In this method of zinc production, the refined zinc is very pure, with the lead being excluded. This change occurred at a time when many users of galvanized sheet, especially those desiring a high quality finish after painting, such as the automotive and appliance industries, needed a non-spangled coating. Removing the lead gave them the product they desired. The amount of lead in the coating for lead-free coatings is less than 0.01%. Lead-free coatings still have a grain pattern that is visible to the unaided eye. Typically, the spangles are about 0.5 mm in diameter and are clearly visible when seen at 5 to 10X. However, the grains no longer grow by a dendritic mode but by a cellular mode of growth. Essentially, the grains of zinc nucleate on the steel surface, and grow outward toward the free surface. The absence of lead takes away the strong driving force for growth in the plane of the sheet, preventing the formation of large spangles. Rapid spangle growth cannot occur and the absence of lead results in the coating appearing uniformly shiny. This non-spangled coating, when combined with temper rolling by the galvanized-sheet producer, can be made very smooth. The large grain boundary depressions and surface relief of a spangled coating are not present. The coating can be painted to give a very smooth, reflective finish. An added advantage of producing a lead-free galvanized coating is that is not susceptible to a problem known as intergranular corrosion. This is a coating failure mechanism in damp environments caused by the lead concentrating at the spangle boundaries.