1.What is the principle behind the gravimetric method for detection?
Sampling: Cut a sample of known area (usually circular or square) from the galvanized coil.
Weighing: Weigh the original total weight of the sample (W1) using a precision balance.
Zinc Stripping: Completely dissolve the zinc layer on the sample surface using a non-corrosive zinc stripping solution (usually a hydrochloric acid or sulfuric acid solution containing corrosion inhibitors).
Re-weighing: Weigh the stripped and thoroughly cleaned and dried steel substrate (W2).
Calculation:
Zinc layer weight = (W1 - W2)
Zinc layer weight per unit area (g/m²) = (W1 - W2) / Sample area
2.What is the principle behind X-ray fluorescence spectrometry?
Excitation: High-energy X-rays are emitted from an X-ray tube and irradiate the moving steel strip surface.
Excitation Fluorescence: When zinc atoms are excited, they release secondary X-rays with specific energies (i.e., characteristic X-ray fluorescence).
Detection and Analysis: A detector receives these fluorescence signals; their intensity is proportional to the mass (weight) of the zinc layer per unit area. By measuring the fluorescence intensity, the thickness of the zinc layer (usually expressed in g/m²) can be calculated in real time.
3.What is the principle behind beta-ray backscattering detection?
Emission: A radioactive source (such as promethium Pm-147 or krypton Kr-85) emits beta rays.
Backscattering: After beta rays strike the steel strip surface, a portion is reflected back (backscattering).
Measurement: A detector measures the intensity of the backscattered rays. Its intensity is related to the atomic number; zinc has a higher atomic number than iron, therefore its backscattering intensity differs. Through calibration, the relationship between backscattering intensity and zinc layer thickness can be established.
4.What is the principle behind magnetic thickness measurement?
Utilizing the principle of magnetic induction, the magnetic attraction or flux between the magnet in the probe and the steel substrate (magnetic material) varies with the thickness of the non-magnetic/weakly magnetic zinc coating. By measuring this change, the thickness of the zinc coating can be deduced.
5.What are the application characteristics of magnetic thickness measurement?
Advantages: Compact and portable instrument, simple operation, fast speed, and low cost.
Disadvantages:
Requires calibration: Calibration is required using standard sheets on uncoated steel substrates and standard sheets of known thickness.
Many influencing factors: Measurement results are affected by substrate thickness, curvature, surface roughness, and probe placement pressure.
Point-based measurement: Only data from a single point can be acquired; multiple, gridded measurements are required to assess uniformity.