1.What are the thickness uniformity detection technologies?
Magnetic Thickness Measurement Method
Principle: Using the principle of electromagnetic induction, the probe measures the change in magnetic resistance between the magnetic substrate and the zinc layer, and converts the coating thickness.
Operation points: The substrate material and surface roughness need to be calibrated;
The distance between measuring points is ≥10mm, and the number of measuring points per surface is ≥5.
Advantages: Portable and fast, suitable for online detection of production lines, with an accuracy of ±1μm.
X-ray fluorescence method
Principle: X-rays excite the zinc layer to produce characteristic fluorescence, and the thickness is calculated by spectral analysis. The content of elements such as Zn and Fe can be detected at the same time.
Operation points:
The sample needs to be flat, and the diameter of the detection area should be ≥3mm;
The calibration curve should cover the thickness range of 0-100μm.
Advantages: Non-destructive detection, multi-layer coating can be measured, suitable for laboratory precision analysis.
2.What are the composition uniformity detection technologies?
Scanning electron microscope - energy spectrum analysis
Principle: SEM observes the surface morphology of the coating, and EDS analyzes the distribution of elements such as Zn, Fe, and Al.
Typical applications: Detecting the composition fluctuation of the alloy layer;
Analyzing the segregation of the coating caused by the uneven Al content in the zinc liquid
Glow discharge spectroscopy
Principle: Glow plasma bombards the coating, and the element depth distribution is analyzed in real time through the spectral intensity.
Key indicators: Fe content fluctuation range in zinc layer ≤0.5%;
Alloy layer thickness difference ≤2μm.
3.What are the common defects and causes of poor uniformity?
Local zinc layer is too thick: uneven zinc liquid temperature leads to excessive growth of local alloy layer during immersion plating;
Component segregation: insufficient stirring of zinc liquid leads to the formation of brittle phase;
Thickness fluctuation: unstable speed when steel plate leaves zinc pot leads to coating thickness difference of >30%.
4.Any suggestions for process improvements?
A mechanical stirring device (speed 10-15rpm) is added to the zinc liquid to make the Al content deviation ≤0.05%;
A double zinc pot design (preheating pot + main plating pot) is adopted to control the temperature fluctuation ≤5℃;
The zinc output speed is adjusted in linkage with the online detection data.
5.What are the testing process and quality control points?
Sampling plan: According to GB/T 2828.1 standard, when the batch size is ≥1000 pieces, 32 pieces are randomly selected and 5 points are tested on each piece;
Data processing: Calculate the thickness average value and standard deviation (σ≤1.5μm is optimal), draw a histogram to analyze the distribution;
Abnormal processing: When the thickness of a certain area exceeds the average value by ±20%, trace the galvanizing process parameters (such as zinc liquid temperature, immersion time.