Q1: What exactly does galvanized layer weight refer to? What role does it play in color-coated steel sheets?
A1: Galvanized layer weight usually refers to the total amount of zinc plating on both sides, measured in grams per square meter (g/m²). It is also commonly represented in the industry by codes such as "Z80" and "Z275". It represents the thickness of the zinc plating layer on the steel sheet surface and is a core technical parameter for measuring the product's corrosion resistance. In color-coated steel sheets, the surface organic coating (paint) initially provides isolation and protection. Once the coating is damaged, the zinc plating layer acts as a sacrificial anode, preferentially corroding itself to protect the steel sheet at cuts and scratches, preventing rust.
Q2: What is the recommended galvanized layer weight for different operating environments?
A2: Environmental corrosivity is the primary determining factor in selection. Generally, the stronger the environmental corrosivity, the higher the required galvanized layer weight. Specific recommendations are shown in the table below:
Environment Type | Typical Scenarios | Recommended Weight for Hot-Dip Galvanizing (GI) | Recommended Weight for Hot-Dip Zinc Aluminum (GL)
Inland Dry Environment | Ordinary factories, warehouses, general industrial plants | 80-120 g/m² (e.g., Z80, Z100) | Not required or selectable based on budget
Medium Corrosivity Environment | High temperature and high humidity areas (e.g., southern regions), industrial areas, livestock farming | ≥140 g/m² (e.g., Z140) | ≥100 g/m² (e.g., AZ100)
High Corrosivity Environment | Coastal areas, chemical plants, smelters, paper mills | ≥180 g/m², strongly recommended 275 g/m² (e.g., Z180, Z275)
Q3: Besides the environment, what other factors must be considered when selecting a substrate?
A3: Besides the environment, the following two key points cannot be ignored:
Substrate type (GI vs. GL): Hot-dip galvanized (GI) offers high cost-effectiveness and is suitable for conventional environments such as inland areas; hot-dip aluminized zinc (GL) has 2-6 times the corrosion resistance of GI. Under the same corrosive conditions, a lower weight can be chosen than GI; for example, GL's 100g/m² can meet the requirements of some high-requirement environments.
Substrate thickness and cut edge protection: For thinner steel plates, the zinc coating weight on one side should be increased accordingly to ensure corrosion protection at the cut edges. An important reference indicator is the "zinc ratio," which is the zinc coating weight on one side (g/m²) divided by the steel plate thickness (mm). To effectively prevent cut edge corrosion, it is recommended to ensure that the "zinc ratio" is greater than 100. For example, for a 0.6mm thick steel plate, the zinc coating weight on one side should be at least 60g/m².
Q4: What are the common standards and conversion relationships for zinc coating weight?
A4: The domestic market mainly follows the national standard GB/T 12754, which has minimum requirements for different substrates under different corrosive environments (e.g., GI minimum requirement is 90g/m²). Internationally accepted standards include ASTM, JIS, EN, etc. Furthermore, the coating weights of GL and GI cannot be directly compared. Under the condition of equivalent corrosion resistance, the weight of GL can be about half that of GI. For example, approximately 140g/m² of GI is approximately equivalent to 75g/m² of GL in terms of corrosion resistance.
Q5: What are some common misconceptions to be wary of when purchasing steel sheets?
A5: Be sure to be wary of the following three points when purchasing:
**Falling into the low-price trap:** Do not focus solely on the price of color-coated steel sheets while ignoring the specific requirements for the weight of the galvanized layer. Some manufacturers may reduce costs by thinning the galvanized layer to a level below the national standard (e.g., only 30g/m² on both sides), which will severely shorten the product's lifespan.
**Confusing substrate types:** Hot-dip galvanized (GI) and hot-dip aluminized zinc (GL) steel sheets have different corrosion resistance and prices. Make sure to clearly specify these differences in the contract and technical documents.
**Ignoring cuts and connectors:** The cuts in the steel sheet are the starting point for corrosion. During installation, the cuts should be treated with necessary anti-corrosion measures. At the same time, anti-corrosion connectors (such as bolts and rivets) of the same or higher grade as the steel sheet should be selected.