The quality requirements for superior grade galvanized steel sheets include specifications, dimensions, surface finish, zinc coating weight, chemical composition, sheet shape, mechanical properties, and packaging.
1. Packaging
There are two types of packaging: galvanized sheets cut to fixed lengths and galvanized sheets in coils. Generally, they are packaged in sheet metal, lined with moisture-proof paper, and secured with iron straps to prevent friction between the inner sheets.
2. Dimensions
Relevant product standards (as listed below) specify the recommended thickness, length, and width of galvanized sheets, as well as their permissible defects. Additionally, the width and length of the sheets and the width of the coils can be determined according to user requirements.
3. Surface Finish
Surface condition varies depending on the coating process, such as ordinary zinc spangle, fine zinc spangle, flat zinc spangle, no zinc spangle, and phosphated surfaces. Galvanized sheets cut to fixed lengths and galvanized coils must not have defects that affect their use, but coils are allowed minor irregularities such as welded areas.
4. Zinc Plating Weight
Zinc plating weight is a widely adopted method for determining the thickness of the zinc layer on galvanized sheets. There are two types: equal zinc plating on both sides (equal thickness galvanizing) and unequal zinc plating on both sides (differential thickness galvanizing). The unit for zinc plating weight is g/m².
5. Mechanical Performance
(1) Tensile Strength Test: Generally, only galvanized sheets used for structural, tensile, and deep drawing applications have tensile strength requirements.
(2) Bending Test: This is an important test for evaluating the performance of thin sheet processing. However, the requirements for various types of galvanized sheets differ across countries. Generally, it is required that after bending the galvanized sheet 180°, the outer coating should not have any zinc layer separation, and the sheet base should not have any cracks or breaks.
6. Chemical Composition
The requirements for the chemical composition of the galvanized substrate vary among countries. For example, Japan has this requirement, but the United States does not. It is generally not required for finished product inspection.
7. Plate shape
There are two objectives in evaluating plate shape: straightness and camber. The maximum allowable values for the straightness and camber of the plate are defined by certain standards.
