Quality Inspection Standards for Galvanized Steel Sheets
Galvanized steel sheets can be classified into various types based on their production and processing methods, including hot-dip galvanized steel sheets, electro-galvanized steel sheets, single or double-sided differentially thick galvanized steel sheets, and alloy composite galvanized steel sheets. Additionally, there are special varieties such as color-coated galvanized steel sheets, printed galvanized steel sheets, and PVC laminated galvanized steel sheets. Furthermore, galvanized steel sheets find wide applications in different fields including general purpose, roofing, building exterior panels, structural use, corrugated sheets, drawing, and deep drawing. For premium-grade galvanized sheets, quality requirements cover multiple aspects such as dimensional specifications, appearance, coating weight, chemical composition, shape, mechanical properties, and packaging.
1. Packaging Methods
Galvanized sheets have two main packaging types: First, cut-to-length sheets, typically packaged with sheet iron wrapping, lined with moisture-proof paper, and secured externally with iron strapping to ensure firmness and reliability, preventing friction between sheets. Second, galvanized steel coils, whose packaging must also ensure stability to protect the product from damage.
2. Specifications and Dimensions
The standard thickness, length, and width of the product, along with their permissible deviations, are clearly stipulated in relevant standards. Additionally, sheet width and length, as well as coil width, can be customized according to user requirements.
3. Surface Appearance
The surface appearance of galvanized sheets varies depending on the coating process, for example, regular spangle, minimized spangle, spangle-free, zinc-phosphated surface, etc. For cut-to-length galvanized sheets and cut lengths from coils, the surface must be free from defects that affect usability. However, coils are permitted to have minor abnormal sections such as certain welded areas.
4. Coating Weight
Coating weight is a key indicator for measuring the zinc layer thickness of galvanized sheets, expressed in g/m². It has two types: uniform coating and differential coating, meaning the same or different coating weights on both sides.
5. Mechanical Properties
The mechanical properties of galvanized sheets include tensile tests and bend tests. Tensile tests are primarily for structural, drawing, and deep-drawing grades; while bend tests are an important measure of the workability of thin sheets. After a 180-degree bend, the outer surface should show no zinc layer detachment, and the substrate must remain intact and undamaged.
6. Chemical Composition
Requirements for the chemical composition of the galvanized substrate vary among countries. For instance, Japanese standards do not include this requirement, while US standards have explicit stipulations. Typically, chemical composition is not a mandatory inspection item for finished products.
