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Thickness measuring is an important process to ensure quality and compliance with regulations. Coatings are applied to provide protection, decoration. Besides coatings provides properties such as conductivity, adhesion, and corrosion resistance. The thickness of the coating affects its performance, durability, and cost-effectiveness.
Measuring coating thickness involves different methods and instruments. Each method offers various accuracy, cost, complexity, and suitability. In this article, we will discuss the techniques for thickness measurement.
Magnetic Induction Method
The magnetic induction method is the most used technique for non-magnetic coatings on magnetics such as steel. It relies on the principle that the coating thickness affects the magnetic field that penetrates the substrate. A magnetic probe is placed on the coating surface, and a magnetic field is generated. The change in the magnetic strength is measured and converted into coating thickness. Conversion is performed using calibration curves or formulas.
The magnetic induction method is fast, and non-destructive. Itcan measure coatings ranging from a few microns to several millimeters. Yet, it may be affected by the substrate properties, surface roughness, and geometry. Also magnetic induction readers may need frequent calibration and verification.
Eddy Current Method
The eddy current method measures the electrical conductivity of the coating and substrate. It uses an electromagnetic coil to generate high-frequency alternating currents. High-frequency current then induces eddy currents in the conductive coating. Interaction between the current and the magnetic field creates a signal. The generated signal is proportional to the coating thickness.
This method is suitable for measuring non-conductive coatings on conductive materials. Aluminum, copper, and brass are some of the coating which can be measured by eddy currents. It can also detect defects such as cracks, pores, and delamination. Yet, it may be affected by the substrate thickness, surface condition, and the coating composition and thickness.
The ultrasonic method is a non-destructive measurement technique. It uses high-frequency sound waves to measure the coating thickness. This method functions by measuring the time of feedback. The emitted sound waves are reflected back from the coating-substrate surface. The delay between the transmitted and received signals is proportional to the coating thickness.
This method can measure both conductive and non-conductive coatings. Plastics, composites, and ceramics are example materials which can be measured by this method. It can also detect defects such as voids, inclusions, and corrosion. Yet, it needs a skilled operator and adequate coupling between the transducer and the surface.
X-Ray Fluorescence Method
The X-ray fluorescence (XRF) method is a non-destructive technique of measurement. It measures the coating thickness and composition using X-ray radiation. It relies on the principle that the atoms in the coating and substrate emit characteristic X-rays. The intensity of the X-rays is proportional to the coating thickness and composition.
The XRF method can measure both thin and thick coatings on various substrates, including metals, plastics, and ceramics. It can also determine the elemental composition of the coating and substrate. Yet, it may be affected by the surface roughness, contamination, and interference from other elements.
The microscopy method is a destructive technique that measures the coating thickness. Microscopy method uses optical or electron microscopy. It involves cross-sectioning the coated substrate, and imaging the section using a microscope. The thickness is determined by measuring the distance between the coating and the substrate.
This method can provide high-resolution images and quantitative measurements. It can also identify defects such as voids, cracks, and adhesion failures. Yet, it may be time-consuming
Coating thickness measurement is a key process to ensure product quality and compliance with standards. However, the correct choice of measurement method is important to receive accurate results.