Q:How to detect the quality of galvanized steel from the surface?
A:Coating integrity
Mis-plating: Observe whether there are exposed areas without galvanizing on the surface of the steel plate (visual inspection or color flaw detection). Miss-plating will cause local rust.
Zinc layer adhesion:
Bending test: Bend the sample 180° to observe whether the zinc layer cracks or falls off;
Impact test: Use a heavy object to impact the surface to detect the zinc layer's ability to resist peeling (applicable to thick-coated products).
Q:How to detect dimensional accuracy?
A:1. Thickness tolerance
According to GB/T 708 standard, the thickness tolerance of cold-rolled galvanized steel sheet is usually ±0.03~±0.1mm (the thinner the thickness, the stricter the tolerance requirement).
Measuring tool: micrometer (accuracy 0.001mm), take 5 points evenly in the width direction of the steel plate for measurement, the difference between the maximum and minimum values should be ≤ the tolerance range.
2. Plate shape and straightness ◦ Visual inspection: The steel plate should have no obvious defects such as wave shape, sickle bend, and scoop bend;
Straightness measurement: Use the wire drawing method or laser measuring instrument to measure the longitudinal curvature of the steel plate (usually ≤2mm/m).
3. Width and length ◦ Width tolerance ±2mm, length tolerance ±5mm (according to order requirements), use a tape measure or laser length measuring instrument for detection.
Q:How to measure coating thickness?
A:Magnetic thickness gauge: uses the principle of electromagnetic induction for rapid measurement (suitable for online detection on the production line);
Weighing method: calculates the thickness by the weight difference before and after the coating is dissolved, which has high accuracy but is a destructive test.
Q:How to detect the composition and structure of the coating?
A:Chemical composition analysis: Use X-ray fluorescence spectrometer (XRF) to detect the content of Zn, Al, Si and other elements in the coating (e.g. hot-dip galvanized layer usually contains 0.1%~3% Al, which can improve corrosion resistance).
Microstructure observation: Observe the cross section of the coating through a metallographic microscope. High-quality coatings should present a uniform zinc-iron alloy layer (thickness of about 1~3μm) without coarse grains or holes.
Q:How to quickly judge the quality?
A:1. Visual initial screening: Observe whether the surface is smooth and has no obvious defects, and the zinc layer is uniform in color (silver gray or slightly blue), without blackening or yellowing.
2. Simple mechanical test: Bend a small sample by hand, and the high-quality plate should not be easy to break, and the zinc layer should not fall off obviously;
3. Check the test report: Require the supplier to provide test reports such as coating thickness, tensile properties, and salt spray test to check whether the data meets the standards.