1.What are the classifications of surface treatment?
Regular Spangle:
Characteristics: Zinc molten metal naturally solidifies to form distinct, large-grained zinc spangle crystals, visible as hexagonal patterns under sunlight.
Gloss: Uneven gloss; different parts of the zinc spangle (nucleus and edges) reflect light differently, resulting in a shimmering, crystalline appearance. This is not a high-gloss surface.
Minimal Spangle:
Characteristics: Zinc spangle growth is suppressed through techniques (such as zinc powder spraying or steam spraying), making the spangles extremely small and almost invisible to the naked eye.
Gloss: More uniform and delicate surface, with a higher and more consistent gloss than regular spangle. It is an ideal substrate for subsequent coating (color coating).
Spangle-Free:
Characteristics: Visible zinc spangles are completely eliminated through further processing (such as finishing).
Gloss: Very uniform surface, exhibiting a matte or satin finish. Gloss can be adjusted within a certain range by adjusting the roller roughness of the finishing machine.
2.How does a smooth surface affect the control of gloss?
Eliminating yield plateaus: Improves the mechanical properties of the material and prevents Lüders bands from forming during stamping.
Improving surface smoothness.
Controlling surface roughness and gloss: By using work rolls with different roughnesses, different surfaces ranging from matte to glossy can be obtained.
The finished surface is typically in a spangle-free or small-spangle-free state.
3.What are the requirements for gloss standards in GB/T 2518-2019 "Continuously Hot-Dip Galvanized and Zinc Alloy Coated Steel Sheets and Strips"?
Surface treatment types: Listed are ordinary surface (N), smooth surface (S), phosphated surface (P), and passivated surface (C).
Surface quality levels: Divided into standard (FA), higher (FB), and high (FC). Higher levels have stricter requirements for surface defects (such as holes, zinc particles, scratches, etc.), but this is not directly equivalent to gloss standards.
4.What are the practical controls and applications of gloss?
For galvanized steel sheets used directly (without color coating):
If the user desires a bright appearance, a process with small zinc spangles and a high-gloss finish will be chosen.
If a low-key, matte finish is desired, a process with no zinc spangles and a low-gloss/rough finish will be chosen.
In this case, the required gloss level can be achieved by agreeing on a sample or specifying the roughness range of the finishing roller.
For galvanized steel sheets used as substrates for color coating:
Gloss is not a critical indicator because paint will be applied subsequently.
The key factors are surface uniformity, cleanliness, and roughness. A uniform, appropriately rough surface with small zinc spangles or no zinc spangles is best for paint adhesion, ensuring the final color-coated sheet's gloss and adhesion.
5.What are the gloss standards for color-coated steel sheets?
Low gloss (G1): Gloss ≤ 40
Medium gloss (G2): 40 < Gloss ≤ 70
High gloss (G3): Gloss > 70