How to Measure the Zinc Coating Thickness of Deep Drawing Galvanized Steel
As a supplier of deep drawing galvanized steel, I understand the crucial role that zinc coating thickness plays in the performance and quality of our products. The zinc coating not only provides corrosion resistance but also affects the formability and overall durability of the steel. In this blog post, I will share some common methods for measuring the zinc coating thickness of deep drawing galvanized steel.
Why Measuring Zinc Coating Thickness Matters
Before delving into the measurement methods, it's important to understand why measuring the zinc coating thickness is so important. The thickness of the zinc coating directly impacts the corrosion protection of the steel. A thicker coating generally provides better corrosion resistance, especially in harsh environments. Additionally, the coating thickness can affect the formability of the steel during deep drawing processes. If the coating is too thick, it may crack or flake off during forming, while a thin coating may not provide adequate protection.
Common Methods for Measuring Zinc Coating Thickness
Magnetic Induction Method
The magnetic induction method is one of the most widely used techniques for measuring the zinc coating thickness on ferromagnetic substrates, such as steel. This method is based on the principle that the magnetic field generated by a probe changes when it comes into contact with a non - magnetic coating (zinc) on a magnetic substrate (steel).
The measurement process is relatively simple. A handheld magnetic induction gauge is placed on the surface of the galvanized steel. The gauge emits a magnetic field, and the change in the magnetic field due to the presence of the zinc coating is measured. The instrument then calculates and displays the coating thickness based on pre - calibrated values.
One of the advantages of the magnetic induction method is its non - destructive nature. It can be used directly on the finished products without causing any damage to the coating or the substrate. It is also relatively quick and easy to use, making it suitable for on - site inspections and quality control during production.
However, this method has some limitations. It requires a flat and smooth surface for accurate measurements. Rough or curved surfaces can lead to inaccurate readings. Also, the presence of contaminants or other non - zinc layers on the surface can affect the measurement results.
Eddy Current Method
The eddy current method is another non - destructive testing technique that can be used to measure the zinc coating thickness on non - ferromagnetic metals or on a zinc - coated steel when the substrate is non - magnetic or when the magnetic properties of the substrate are not well - defined.
When an alternating current is passed through a coil in the eddy current probe, it generates an alternating magnetic field. When the probe is brought close to the zinc - coated surface, eddy currents are induced in the zinc coating. These eddy currents, in turn, generate their own magnetic fields that interact with the primary magnetic field of the probe. The change in the impedance of the coil due to the interaction with the eddy currents is measured and used to determine the coating thickness.
Similar to the magnetic induction method, the eddy current method is quick and non - destructive. It can be used on a variety of shapes and sizes of galvanized products. However, like the magnetic induction method, it also requires a clean and smooth surface for accurate measurements. Additionally, the measurement accuracy can be affected by factors such as the conductivity of the zinc coating and the substrate, as well as the presence of other conductive layers or contaminants.
Gravimetric Method
The gravimetric method is a destructive testing technique that provides highly accurate measurements of the zinc coating thickness. In this method, a sample of the galvanized steel is cut from the product. The sample is then weighed to determine its initial mass.
Next, the zinc coating is removed from the sample using a chemical solution. After the coating is completely removed, the sample is washed, dried, and weighed again to obtain the mass of the bare substrate. The difference in mass between the initial and final weights represents the mass of the zinc coating.
The coating thickness can then be calculated using the density of zinc and the surface area of the sample. The formula for calculating the coating thickness (t) is (t=\frac{m}{\rho\times A}), where (m) is the mass of the zinc coating, (\rho) is the density of zinc, and (A) is the surface area of the sample.
The gravimetric method is considered the most accurate way to measure the zinc coating thickness because it directly measures the mass of the zinc coating. It is often used as a reference method for calibrating other non - destructive testing instruments.
However, its destructive nature is a major drawback. It cannot be used on finished products that need to be kept intact. It is also time - consuming and requires a laboratory setting for accurate chemical treatment and weighing.
Considerations for Measuring Zinc Coating Thickness in Deep Drawing Galvanized Steel
When measuring the zinc coating thickness of deep drawing galvanized steel, there are some additional considerations.
During the deep drawing process, the zinc coating may be deformed along with the steel substrate. This deformation can cause local variations in the coating thickness. Therefore, it is important to take multiple measurements at different locations on the formed part to get a representative value of the coating thickness.
Also, the formability of the zinc coating can affect the measurement results. If the coating has cracked or flaked off during deep drawing, the measured thickness may not accurately represent the original coating thickness. In such cases, it may be necessary to use a combination of measurement methods to get a more comprehensive understanding of the coating condition.
Zinc Aluminum Magnesium Coated Steel
In addition to traditional zinc - coated steel, Zinc Aluminum Magnesium Coated Steel is gaining popularity in the market. This type of coating offers enhanced corrosion resistance compared to pure zinc coatings. The measurement methods for zinc aluminum magnesium coated steel are similar to those for traditional galvanized steel. However, due to the different chemical composition and properties of the coating, the calibration of the measurement instruments may need to be adjusted accordingly.
Conclusion
Measuring the zinc coating thickness of deep drawing galvanized steel is essential for ensuring the quality and performance of the products. Each measurement method has its own advantages and limitations, and the choice of method depends on various factors such as the nature of the substrate, the shape and size of the product, and the required accuracy of the measurement.
As a supplier of deep drawing galvanized steel, we are committed to providing high - quality products with accurate and consistent zinc coating thickness. If you are interested in our deep drawing galvanized steel products or have any questions about zinc coating thickness measurement, please feel free to contact us for further discussion and procurement negotiations.
References
- ASTM International. ASTM A90/A90M - 21, Standard Test Method for Weight [Mass] of Coating on Iron and Steel Articles with Zinc or Zinc - Alloy Coatings.
- ISO 2178:2016, Non - magnetic coatings on magnetic substrates — Measurement of coating thickness — Magnetic method.
- ISO 2360:2017, Non - conductive coatings on non - magnetic electrically conductive base metals — Measurement of coating thickness — Eddy - current method.