The corrosion resistance and service life of color-coated sheets depend crucially on whether the zinc coating and paint film thickness meet the standards. As a procurement, quality inspection, or production professional, have you ever encountered these confusions:
- How to accurately calculate the weight of zinc coating?
- How to standardize the measurement of paint film thickness?
- How to convert indicators under different standards?
Today, we will use the easiest-to-understand way to help you fully understand the calculation methods of these two key indicators of color-coated sheets!
I. Calculation of Zinc Coating
01 Calculation Method of Zinc Coating Weight (g/m²)
Core Formula: Zinc Coating Weight = (Weight Before Zinc Removal − Weight After Zinc Removal) / Sample Area
Operation Steps:
- Sampling: Cut a standard sample of 10cm × 10cm (area: 0.01 m²).
- Weighing: Use an analytical balance (0.1mg precision) to measure the initial weight W1 (e.g., 50.235g).
- Zinc Removal: Dissolve the zinc coating with 1:1 hydrochloric acid (Note: Avoid excessive corrosion of the base plate).
- Re-weighing: Measure the weight after zinc removal W2 (e.g., 49.835g).
- Calculation: (50.235 − 49.835) / 0.01 = 40 g/m²
02 Conversion Method of Zinc Coating Thickness (μm)
Thickness (μm) = Weight (g/m²) / 7.14
(Based on the zinc density of 7.14 g/cm³)
Example: If the measured zinc coating weight is 60 g/m², then the thickness = 60 / 7.14 = 8.4 μm
II. Calculation of Paint Film Thickness
01 Direct Measurement Method
- Use a magnetic thickness gauge for steel base plates.
- Use an eddy current thickness gauge for aluminum base plates.
Key Calculation Points:
- Measure 5 different positions.
- Exclude the maximum and minimum values.
- Calculate the average value of the remaining 3 points.
02 Weight Difference Method
Film Thickness (μm) = (Weight After Painting − Weight After Paint Removal) / (Area × Paint Density)
Note: The density of ordinary polyester paint is about 1.2–1.5 g/cm³
III. Key Indicator Comparison Table
| Quality Grade |
Zinc Coating Requirement (g/m²) |
Corresponding Thickness (μm) |
Paint Film Thickness (μm) |
| Standard Grade |
≥60 |
8.4 |
15-20 |
| Premium Grade |
≥80 |
11.2 |
20-25 |
| Superior Grade |
≥120 |
16.8 |
25-35 |
Mastering these calculation methods allows you to easily control the quality of color-coated sheets!
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