As a supplier of galvanized parts, I often encounter questions from customers about how to measure the thickness of the galvanized layer on these parts. The thickness of the galvanized layer is a critical parameter that directly impacts the corrosion resistance and service life of the parts. In this blog, I will share several methods for measuring the galvanized layer thickness, their advantages and disadvantages, and some practical tips for ensuring accurate measurements. Galvanized Parts
Destructive Measurement Methods
Gravimetric Method
The gravimetric method is one of the most traditional and accurate ways to measure the thickness of the galvanized layer. It involves weighing the part before and after the removal of the galvanized layer. The difference in weight is then used to calculate the thickness.
First, the part is thoroughly cleaned to remove any dirt, grease, or other contaminants. Then, it is weighed accurately using a high – precision balance. Next, the galvanized layer is chemically removed from the part using a suitable acid solution, such as hydrochloric acid with an inhibitor to prevent the base metal from being attacked. After the galvanized layer is completely removed, the part is washed, dried, and weighed again.
The thickness of the galvanized layer can be calculated using the following formula:
[t=\frac{W}{\rho\times A}]
where (t) is the thickness of the galvanized layer, (W) is the weight of the galvanized layer (the difference in weight before and after removal), (\rho) is the density of zinc ((7.14\ g/cm^{3})), and (A) is the area of the part from which the galvanized layer was removed.
The advantage of the gravimetric method is its high accuracy. It provides a direct measurement of the mass of the zinc coating, which can be used to calculate the thickness precisely. However, the main disadvantage is that it is a destructive method. Once the galvanized layer is removed, the part is no longer usable for its intended purpose, making it unsuitable for quality control in large – scale production where non – destructive testing is preferred.
Microscopic Method
The microscopic method involves cutting a cross – section of the galvanized part and examining it under a microscope. This method allows for a direct visual measurement of the thickness of the galvanized layer.
First, a sample is carefully cut from the part using a suitable cutting tool, such as a saw or a wire cutter. The cut surface is then polished to a smooth finish using a series of abrasives, starting from coarse to fine. After polishing, the sample is etched with a suitable etchant to reveal the boundaries between the base metal and the galvanized layer.
The etched sample is then placed under a microscope, and the thickness of the galvanized layer is measured at several points along the cross – section. The average of these measurements is taken as the thickness of the galvanized layer.
The microscopic method provides a direct and accurate measurement of the galvanized layer thickness. It can also reveal the structure of the galvanized layer, such as the presence of different zinc – iron alloy layers. However, similar to the gravimetric method, it is a destructive method. Cutting and preparing the cross – section are time – consuming processes, and the sample cannot be used again after the measurement.
Non – Destructive Measurement Methods
Magnetic Induction Method
The magnetic induction method is a widely used non – destructive technique for measuring the thickness of the galvanized layer on ferrous substrates. It is based on the principle that the magnetic field generated by a magnetic probe is affected by the presence of the non – magnetic galvanized layer on the magnetic base metal.
The measuring instrument consists of a magnetic probe and an electronic unit. The probe is placed on the surface of the galvanized part, and the magnetic field generated by the probe interacts with the base metal. The presence of the galvanized layer changes the magnetic field strength, and this change is measured by the electronic unit. The instrument then converts the measured magnetic field change into the thickness of the galvanized layer.
The advantage of the magnetic induction method is that it is non – destructive, fast, and easy to use. It can be used on the production line for real – time quality control. However, its accuracy can be affected by factors such as the surface roughness of the part, the curvature of the surface, and the presence of magnetic contaminants on the surface.
Eddy Current Method
The eddy current method is suitable for measuring the thickness of the galvanized layer on non – ferrous substrates. It works on the principle of electromagnetic induction. When an alternating current is passed through a coil in the probe, an alternating magnetic field is generated. This magnetic field induces eddy currents in the conducting substrate.
The presence of the non – conducting galvanized layer on the substrate affects the flow of eddy currents. The change in the eddy current characteristics, such as impedance, is measured by the instrument. The instrument then converts this change into the thickness of the galvanized layer.
Similar to the magnetic induction method, the eddy current method is non – destructive, fast, and can be used for on – line quality control. However, it also has limitations. The accuracy can be affected by factors such as the electrical conductivity of the substrate, the surface finish, and the shape of the part.
Practical Tips for Accurate Measurements
- Calibration: Whether using a magnetic induction or eddy current instrument, regular calibration is essential. Calibration should be done using standard samples with known galvanized layer thicknesses.
- Surface Preparation: The surface of the part should be clean and free of dirt, grease, and rust before measurement. Surface roughness can also affect the measurement accuracy, so it is advisable to smooth the surface if necessary.
- Multiple Measurements: To ensure accuracy, multiple measurements should be taken at different locations on the part. The average of these measurements should be used as the final result.
- Environmental Conditions: Temperature and humidity can affect the measurement results, especially for electronic measuring instruments. It is recommended to perform measurements under stable environmental conditions.
Conclusion
As a supplier of galvanized parts, understanding how to measure the thickness of the galvanized layer is crucial for ensuring the quality of our products. Different measurement methods have their own advantages and disadvantages, and the choice of method depends on various factors, such as the type of substrate, the required accuracy, and whether the part can be damaged during measurement.
Galvanized Steel Coil We are committed to providing high – quality galvanized parts with the appropriate galvanized layer thickness to meet the requirements of our customers. If you are interested in our products or have any questions about the measurement of the galvanized layer thickness, please feel free to contact us for further discussion and potential procurement opportunities.
References
- ASTM A90/A90M – 19 Standard Test Method for Weight [Mass] of Coating on Iron and Steel Articles with Zinc or Zinc – Alloy Coatings
- ISO 1461:2009 Hot – dip galvanized coatings on fabricated iron and steel articles — Specifications and test methods
- BS EN ISO 2178:2016 Non – magnetic coatings on magnetic substrates — Measurement of coating thickness — Magnetic method
Gnee Steel (Tianjin) Co., Ltd.
Gnee Steel (Tianjin) Co., Ltd. is one of the most professional galvanized parts manufacturers and suppliers in China, specialized in providing high quality products with low price. We warmly welcome you to wholesale cheap galvanized parts in stock here and get free sample from our factory. Also, customized service is available.
Address: No.4-1114, Beichen Building, Beicang Town, Beichen District, Tianjin, China
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